The manufacture of sizing agents of the above-mentioned type and their use in the sizing of paper are known in the art. Thus, a process for the manufacture of such cationic sizing agents is described in Unexamined West German Patent Application DE-OS 1,570,914. The sizing agents produced in this manner, however, tend to gel and therefore must be treated with acid after their manufacture; this necessitates the use of alkali shortly before or during the sizing process.
If an excessively low molar amount of maleic anhydride is used relative to the alpha-olefin, sizing agents are obtained that are soluble or dispersible only with difficulty in water. Excess maleic anhydride produces inferior or mediocre sizing agents. Moreover, the process can be used only in a relatively narrow range of copolymer molecular weights. If copolymers with a molecular weight greater than 5000 are used, the product's tendency to gel increases rapidly.
The storage stability of the product leaves much to be desired; in addition, the epoxide groups tend to hydrolyze to a considerable extent so that, before use of the product, the alcohol groups formed by hydrolysis must again be transformed into epoxide groups during sizing by way of an etching agent.
For this reason, there still is a need for an improved process for the manufacture of such cationic sizing agents, which are distinguished by improved properties.